The present invention relates to equipment for automatically sorting objects, such as pistachio nuts; and more particularly to such equipment which sorts the objects based on sound.
Pistachio nuts are graded and sorted based on whether or not the shell has split open. A typical harvest of pistachio nuts comprises 17% with a closed shell, 5% with a thinly split shell, and 78% with a fully open shell. Nuts with closed shells have low consumer acceptance because they are difficult to open and may contain immature kernels. Thus closed shell pistachio nuts are less valuable than those with open shells.
The pistachio industry currently utilizes a variety of methods and equipment to sort lesser quality nuts from the high grade product. A common mechanical device has a rotating drum with pins projecting inward from the interior surface. As the pistachio nuts tumble in the drum, those with open shells become lodged on the pins and carried upward. At the top of the drum a brush removes the open nuts from the pins and those nuts fall onto a collector. The pins can not impale the pistachio nuts with closed shells and these nuts pass through the drum into another collector.
Furthermore, approximately five to ten percent of open shell pistachio nuts are incorrectly classified by the mechanical sorters as having a closed shell. Such incorrect classification costs the U.S. pistachio industry several millions of dollars a year.
Machine vision systems also have been proposed for sorting pistachio nuts. However, these systems are relatively expensive and have a classification accuracy similar to that of mechanical sorting machines. Thus vision systems may not be economically justified.
Therefore, there remains a need to increase the accuracy of the sorting process for closed shell pistachio nuts.
The present novel object sorting method commences by creating an impact between the object and a body, such as by bouncing the object off the body. Preferably the body has a sufficiently large mass that it does not emit sound due to the impact. However, the object does emit a sound upon impact and a transducer produces an electrical signal representing that sound.
The electrical signal is analyzed to determine a characteristic of the electrical signal which indicates a trait of the object on which sorting is to be based. For example, this method has application in sorting pistachio nuts based on whether their shells are open or closed. In response to the results of the analysis the object is directed along a selected a path.
Analysis of the electrical signal preferably involves integrating a magnitude of the electrical signal, deriving a gradient for a portion of the electrical signal, or both of those arithmetic operations. In the preferred processing technique, the electrical signal is digitized into a plurality of signal samples. Then the absolute value of selected signal samples, acquired during a predefined interval after the impact, are integrated to produce an integration value. In addition, that signal samples which have a magnitude in a first predetermined range of values and a gradient in a second predetermined range of values are counted to produce a first count value. A second count value may be produced by counting the signal samples which have a magnitude in a third predetermined range of values and a gradient in a fourth predetermined range of values. The integration value and the first and second count values then are utilized to classify the object and the classification determines along which path to direct the object.